The present inventon relates to straight line shear mechanisms and more particularly to an improved drive assembly therefor.
U.S. Pat. No. 4,215,611 discloses an apparatus for straight line shearing of molten glass wherein upper and lower shear blade assemblies are each reciprocably mounted on carriage members, the upper and lower carriage members being driven by a pneumatic cylinder assembly and rack an pinion arrangement. As illustrated in FIGS. 1 and 2 of the U.S. Pat. No. '611, and discussed at column 9, lines 8-66, one of the shear blade carriage arms (or "flange portions") is coupled to a forward portion of the operating rod driven by the pneumatic cylinder assembly, while the other carrige arm is indirectly driven in the opposite direction by means of a parallel rack and pinion linkage between such carriage arm and a rear portion of the operating rod. In both cases, the flange portion, or carriage arm, is secured to the driving rod or rack using washers, lock washer, and a nut member to secure the connection. The carriage arms are in turn connected to the shear blade carriages via tubular portions of the carriages which are slidingly mounted on guide rods, the opposite ends of the carriage being slidingly mounted on a guide rail. Thus, the shear blades are reciprocated between open and shearing positions along an axis parallel to the axes of the guide rods, and ideally, to the axes of the operating rod and racks.
In practice, such straight line shearing mechanisms have sometimes encountered premature wear of parts due to the rigid connection between the drive rod and rack and the shear blade carriages. This rigid connection did not permit compensation for any non-parallelism of the drive rods to the guide rods. Furthermore, in assembling a shear mechanism, it was difficult to assure a proper alignment of the drive rods, carriage arm, and the complex shear blade carriage assemblies, inasmuch as the dimensional tolerances of these interconnected parts were such that misalignment could occur if the parts were not chosen and assembled with great care. This latter problem arose from the intolerance of the rack rodcarriage arm joints to radial misalignment.
Commonly assigned U.S. Pat. No. 4,699,643 discloses various improved drive assemblies for straight line shears, all of which incorporate a drive pinion for reciprocating racks which are secured to the shear blade carriages. Certain disclosed embodiments incorporate a fluidic drive source in combination with an electric servo motor, while the embodiment of FIG. 1 relies upon the servo motor alone to directly drive the pinion gear. All of these embodiments share the feature that the drive rack rods are fixedly mounted to arms extending from the shear blade carriages, and share the shortcomings described above.
Accordingly, it is a principal object of the invention to provide an improved drive assembly for a straight line shear mechanism of the type utilizing reciprocating rods to drive the parallel-mounted carriages housing the shear blade assemblies. In particular, it is desired to avoid premature wear and dimensional tolerance problems encountered in prior art systems of this type.